Method and apparatus for coupling ultrasound between an ultrasonic transducer and an object

ABSTRACT

A method and apparatus are disclosed for coupling ultrasound between an ultrasonic transducer and an object. A fluid cavity in an upper chamber has an inlet for receiving a flow of coupling fluid, a first aperture for admitting the ultrasonic transducer into the fluid cavity and a second aperture for dispensing coupling fluid from the fluid cavity to the object. The first and second apertures may be sized to restrict flow of coupling fluid from the fluid cavity. The focus of the ultrasound transducer may be varied by moving the ultrasonic transducer relative to the upper chamber.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of U.S. patent applicationSer. No. 10/387,881 filed Mar. 13, 2003 and titled “Ultrasonic TestChamber for Tray Production System and the Like”.

FIELD

This invention relates generally to the field of ultrasonic scanning.More particularly, this invention relates to a method and apparatus forproviding acoustic coupling between an ultrasonic scanner and a testpiece.

BACKGROUND

Non-destructive inspection of parts has been used for many years. Morerecently, ultrasonic inspection has been extended to small parts such asintegrated circuits or other electronic components. During themanufacture of integrated circuits (ICs), the parts are often looselyarranged in trays or holders to facilitate transfer of the parts throughthe production process. In order to prevent delays in the productionprocess, an ultrasonic tester that can accommodate trays of parts isrequired. An ultrasonic tester may include three sections. The firstsection is a de-bubbling area where the parts in the carriers are wettedand air bubbles are removed. The normal convention is to submerge theparts and ‘wiggle’ them to remove the air bubbles. The second section isa scanning station where wetted and bubble free parts are ultrasonicallyscanned. In order to complete the scan in a short time, the ultrasonictransducer must be moved across the parts at high speed in closeproximity to the parts. The result is a motion in the fluid that tendsto move the parts in the carriers or dislodge them from the carrier. Thethird section is a drying area, where a gas stream is used to dry anyresidual coupling fluid from the parts. Typically compressed and/orheated air is directed across the parts. Each of these processes tendsto dislodge the parts when they are loosely arranged in a tray orcarrier.

There is a continuing drive towards the use of higher frequencyultrasound, which provides greater resolution of the scanned image.Since higher frequency ultrasound is attenuated in very short distances,it is necessary to move the ultrasonic transducer very close to theobject being scanned. Conventional, non-immersion, transducer may befitted with squirters or bubbles that produce a column of coupling fluidbetween the transducer and the part. These do not allow the transducerto be moved close enough to the part to prevent the attenuation of veryhigh frequency ultrasound.

SUMMARY

The present invention relates generally to ultrasonic scanning. Objectsand features of the invention will become apparent to those of ordinaryskill in the art upon consideration of the following detaileddescription of the invention.

The invention relates to methods and apparatus for coupling ultrasoundbetween an ultrasonic transducer and an object. A fluid cavity in anupper chamber has an inlet for receiving a flow of coupling fluid, afirst aperture for admitting the ultrasonic transducer into the fluidcavity and a second aperture for dispensing coupling fluid from thefluid cavity to the object. The first and second apertures may be sizedto restrict flow of coupling fluid from the fluid cavity. The focus ofthe ultrasound transducer may be varied by moving the ultrasonictransducer relative to the upper chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, however, as well asthe preferred mode of use, and further objects and advantages thereof,will best be understood by reference to the following detaileddescription of an illustrative embodiment when read in conjunction withthe accompanying drawing(s), wherein:

FIG. 1 is an exploded view of an ultrasonic test chamber in accordancewith certain embodiments of the present invention.

FIG. 2 is a further view of the ultrasonic test chamber shown in FIG. 1.

FIG. 3 is a diagrammatic representation of an upper chamber of anultrasonic test chamber.

FIG. 4 is a diagrammatic representation of a lower chamber ultrasonictest chamber bottom.

FIG. 5 is a cross sectional diagram of an ultrasonic test chamber inaccordance with certain embodiments of the present invention.

FIG. 6 is a diagrammatic representation of an array of spring fingers inaccordance with certain embodiments of the present invention.

FIG. 7 is a cross sectional diagram of an ultrasonic test chamber inaccordance with further embodiments of the present invention.

FIG. 8 is a cross sectional diagram of an ultrasonic test chamber inaccordance with still further embodiments of the present invention.

FIG. 9 is top view of a further embodiment of an upper chamber.

FIG. 10 is a sectional view of the upper chamber shown in FIG. 9.

FIG. 11 is a front view of the upper chamber shown in FIG. 9.

FIG. 12 is a side view of scanning apparatus using the upper chambershown in FIG. 9.

FIG. 13 is top view of a still further embodiment of an upper chamber.

FIG. 14 is a sectional view of the upper chamber shown in FIG. 13.

FIG. 15 is a sectional view of a further embodiment of an upper chamber.

DETAILED DESCRIPTION

While this invention is susceptible of embodiment in many differentforms, there is shown in the drawings and will herein be described indetail one or more specific embodiments, with the understanding that thepresent disclosure is to be considered as exemplary of the principles ofthe invention and not intended to limit the invention to the specificembodiments shown and described. In the description below, likereference numerals are used to describe the same, similar orcorresponding parts in the several views of the drawings.

One aspect of the present invention is a method and a system forultrasonic scanning of parts in which coupling fluid is used to holdparts in a parts holder or tray. A further aspect of the invention ismethod and system for holding parts in a parts holder while bubbles areremoved from parts before they are scanned. Still further aspects of theinvention will be apparent from the following detailed description ofillustrative embodiments.

In one embodiment, the ultrasonic test chamber of the present inventionincludes three functional sections: a de-bubbling station, a scanningstation and a dryer. FIG. 1 shows an exploded view of an exemplary testchamber 100 in accordance with the invention. The test chamber comprisesa lower chamber 110 and an upper chamber 102. The chambers are held by aframe or housing (not shown) so that the gap between the two chambersmay be adjusted to accommodate trays of varying thickness. In thisembodiment, the lower chamber is fixed and the upper chamber may beraised or lowered. The upper chamber houses a moveable plate or scanningbar 104, the bottom of which is flush with the bottom of the upperchamber. A first ultrasonic transducer is mounted in the scanning barand can be independently moved up or down (relative to the lower chamberand relative to the scanning bar) to place the transducer at the properdistance from the parts. During operation, a parts tray 106 is passedbeneath the transducer and plate. A second ultrasonic transducer 108 maybe mounted in the lower chamber 110 beneath the tray of parts 106, sothat transmission of ultrasound through the parts may be measured. Thefirst or second transducers may, for example, comprise a single elementtransducer having a spot, line or flat focus, an array of transducers,one or more array transducers or a combination thereof. The arrays maybe line arrays having a single dimension, or area arrays having twodimensions. Example transducers include the Panametrics V313 crystaltransducer, the Sonix MSIC-75M S-12 polymer transducer, the PanametricsV3815 crystal, delay-line transducer, the Panametrics A334S-SUpaintbrush transducer, the Krautkramer linear array and the Imperium DAVarea array.

An assembled ultrasonic test chamber 100 is shown in FIG. 2. The upperchamber 102 is supported by a frame (not shown) so that the moveableplate or scan bar (104 in FIG. 1) is in close proximity to the uppersurface of the parts in the tray of parts 106. The tray of parts 106 ismoved in the direction of arrow 204 along a track, entering the rightside of the chamber in the figure and exiting the left side. The traymay be propelled along the track by an arm connected to a screw drive,for example. The upper and lower chambers are kept filled with acoupling fluid. Fluid is added at rate sufficient to compensate for thefluid lost through openings in the upper and lower chambers. Spilledfluid may be collected in a reservoir 202 and used to the refill thechambers. The re-filling can be performed by a pump so that fluid isre-circulated from the reservoir to the upper and lower chambers. Inthis manner, the tray of parts may be maintained in a substantiallyhorizontal position.

Fluid flow through the tray of parts is restricted, so fluid may beadded to the tray from the upper chamber at a rate sufficient tomaintain sufficient fluid in the tray to permit acoustic coupling of theultrasonic beam to the top of the parts in the tray. If measurement oftransmission through the part is not required, the lower chamber may beomitted or replaced with a fluid-capture tray. A more detailed view ofthe upper chamber 102 is shown in FIG. 3. The chamber is viewed fromabove. In use, the tray of parts first passes below a region ofperforations or holes 302. In a further embodiment, the region 302 maycontain a single slot. Region 302 is the de-bubbling region. Fluid ispassed from below the parts and directed toward the underside of theparts so as to remove air bubbles. Excess fluid passes through theperforations or one or more slots 302 and enters the upper chamber.Additional fluid may be added to the upper chamber as required. Theperforations or slots are sized so as prevent the parts from beingdislodged by the fluid flow. Excess fluid may escape through one or morechannels 304, 306, 308, 310, or through drain pipes (not shown). A track312 is provided to guide the scanning bar 104. The scanning bar slidesfrom left to right and right to left with the first transducer as ittraverses the parts in the tray. The ultrasonic beam or transducerpasses through opening 314. The parts in the tray are held in place bythe scanning bar. In a further embodiment, the de-bubbling area and thescanning area may be separated.

A more detailed view of the lower chamber 110 is shown in FIG. 4. Thechamber is viewed from above. In use, the tray of parts enters on theright of the figure, moving in the direction of arrow 410. The lowerchamber is positioned below the tray of parts 106 (not shown). The trayof parts moves along a track. One rail of the track lies in the slotbetween openings 402 and 406, the other lies in the slot between opening404 and 408. In the embodiment shown in FIG. 4, the lower tray issymmetric so that parts may enter from the left or the right. If partsenter from the left, the upper chamber is rotated through 180°. Thefollowing description assumes that trays enter from the right in thefigure. Chamber 430 is a copy of chamber 428 and is included to permitreversal of the tray movement. It is not necessary. De-bubbling chamber424 is positioned below the de-bubbling region (302) of the upperchamber. Fluid is injected into the de-bubbling chamber 424 through hole412. The fluid may be injected at multiple locations. The injected fluidserves to dislodge air bubbles adhering to the underside of the parts inthe tray. The tray then passes over raised region 416. Preferably theraised region is a substantially planar surface. This surface preventsthe turbulence from the fluid in chamber 424 from reaching the scanningregion, it also tends to reduce fluid flow, facilitating the ultrasoniccoupling between the transducer and the parts in the tray. The scanningregion may be above the raised region 416 or to the left of the raisedregion. If a second transducer is employed, it may be embedded in theraised region or positioned immediately to the left of the raisedregion. Drain chamber 426 is positioned after the scanning region. Fluidis drained from this region through opening 414. The region willtypically contain both fluid and air, and will allow the underside ofthe parts to begin to dry. Fluid flows from the de-bubbling chamber 424to the drain chamber 426, thereby maintaining a flow of fluid from rightto left across the raised region 416. This flow, combined with thecolumn of fluid above the parts being scanned, helps to keep the partsin place. Finally the tray of parts enters the drying region abovechamber 428. Air suction may be applied at opening 429 to help hold theparts in place. The parts are then dried by an air knife, hot air, abrush or by wicking materials (or a combination thereof). The brush orwicking materials are attached to the top side of the lower chamber orto the support frame. Side chambers 418 and 420 collect fluid spilledfrom the sides of the center chambers (424 and 426) and contain drainholes (422 for example) to allow the spilled fluid to be captured in thereservoir.

In a further embodiment, the upper and lower chambers may be integrated,and height of the flat plate varied to accommodate trays of varyingthickness.

FIG. 5 shows a cross-sectional diagram of an exemplary ultrasonic testchamber. A vertical cross-sectional along the axis of motion of theparts tray 106 is shown. The parts tray moves from left to right in thefigure. The lower chamber 110 includes a de-bubbling chamber 424 withopening 412 to receive a flow of fluid. In this embodiment, a secondtransducer 502 is embedded in the raised region 416 to permitthrough-transmission measurements. The drying chamber 426 includesopening 414 where air suction may be applied to hold the parts in placewhile they are dried. The upper chamber 102 includes at least oneopening 302 through which fluid from the de-bubbling chamber passes. Themoving flat plate or scanning bar 104 includes an opening to accommodatethe first transducer. A brace or bracket 504 may be used to preventmovement of the flat plate in directions other than the scan direction.Preferably the scan direction is in a horizontal plane perpendicular tothe motion of the tray, although skewed scan directions may be used. Aset of spring fingers 506 may be used to hold the parts in place whilescanning is performed. The spring fingers 506 are attached to the upperchamber 102 and extend downwards and in the direction of motion of thetray. As the tray passes under the spring fingers they are displacedupwards and exert a downward spring force on the parts in the tray. Abrush or wicking material 508 is attached to the lower chamber to removewater droplets from the bottom surface of the parts in the tray.

A more detailed view of the spring fingers 506 is shown in FIG. 6. Inthis embodiment, a sheet of metal 602 is bent to form an angle. Slots604 are formed in the metal on one side of the fold. The materialbetween the slots forms the spring fingers. Projection 606 may beincluded to facilitate attachment of the set of the spring fingers tothe upper chamber.

A more detailed description of the operation is given below, togetherwith some alternative embodiments.

DE-BUBBLING AREA. The de-bubbling area is where the parts in thecarriers are wetted and air bubbles are removed. Several aspects of thede-bubbling area are now described.

Side Fluid Penetration. The test chamber of the present invention ispartially filled with a coupling fluid, such as water, to facilitatecoupling of the ultrasonic beam to the part under test. The test chamberhas one or more openings in the sides, below the level of the fluid, toallow a parts carrier to passing into the chamber. In one embodiment,this opening is the gap between the upper and lower chambers. Sincefluid will leak from the opening, additional fluid is passed into thechamber to maintain the fluid level. Preferably, the fluid leaking fromthe one or more openings is collected and returned to the chamber. Thecarrier does not have to be raised or lowered, so the system iscompatible with production line configurations and handling equipment.

Water Jet. To remove any air bubbles adhering to the parts, a stream ofwater or other fluid is forced across the parts. Preferably, the flow ofwater is from bottom to top because that is the directions the airbubbles will float when separated from the part or carrier.

Perforated or Slotted Cover. In the case where the water jet is flowingupward, the water will tend to dislodge the parts from the carrier. Aperforated or slotted cover is used to hold the parts in the carrier.The holes are large enough to let water and air bubbles pass but smallenough so that parts can not pass or be dislodged.

SCANNING STATION. The scanning station is where wetted and bubble freeparts are ultrasonically scanned. The ultrasonic transducer is movedacross the parts at high speed in close proximity to the parts. Theresult is a motion in the fluid that tends to move the parts in thecarriers or dislodge them from the carrier. For though-transmission (TT)tests, separate transducers or arrays of transducers are used above andbelow the carrier. The scanning station of the present invention usesone or more of the following approaches to hold the parts in the holder:

Carriers with Retaining Clips. In a first embodiment of the presentinvention, a carrier with retaining clips is used to prevent the partsin the carriers from being dislodged. In some areas of the semiconductorpart manufacturing process, it is advantageous to hold the parts in acarrier with a retaining clip. For example, the Auer Companymanufactures metal carriers commonly referred to as boats that haveretaining clips (For example, Auer part number A27150-001 manufacturedin 9/00 per drawings 110892 Rev. B). Boats can be used in curing ovensand other stages of semiconductor manufacturing. Current practice is toremove the parts from these “boats” and place them in JEDEC trays beforescanning ultrasonically. By scanning the parts in the “boats” the partsdo not have to be moved to another carrier and the parts are held inplace during the ultrasonic scan.

High Pressure above Carrier. In one embodiment of the invention, fluidis added to the parts carrier from above. The fluid is added at one ormore positions away from the scanning area, so that fluid flow does nottend to dislodge the parts. Furthermore, since flow through the partscarrier is restricted, the static fluid pressure above the parts ishigher than the pressure below the parts. This results in a net downwardforce acting to hold parts in the part carrier. Thus, the coupling fluidtends to hold the parts in place rather than to dislodge them.

Low Pressure under Carrier. Because any motion in the fluid (caused forexample by transducer movement) around the parts may tend to move thepart in the holder during the scan (which results in a blurredultrasonic image) or dislodge the part entirely from the holder, it isdesirable to have some type of force holding the parts in to holder.Since materials other than the coupling fluid (typically de-ionizedwater) will have different acoustic impedances and degrade theultrasonic image, it is desirable for this force to be applied via thecoupling fluid. In one embodiment of the invention a fluid flow ismaintained below the carrier. This results in a net downward force onthe parts that will tend to hold the parts in the carrier. The flow ismaintained across the raised region of the lower chamber.

FIG. 7 is a simplified cross-sectional diagram of an ultrasonic testchamber in accordance with a further embodiment of the presentinvention. In this embodiment, the scanning station comprises a tank 702containing coupling fluid 704. A tray 706 supports a number of objects708. Typically, the objects are loosely held. An ultrasonic transducer710 is used to scan the objects. A second transducer (not shown) may beused to sense the ultrasound transmitted through the objects. The holderor tray 706 is held above a surface 712. Preferably, the surface is flatin the direction of the scan line of the ultrasonic transducer 710, butmay be curved in the other direction to facilitate fluid flow. A flow ofcoupling fluid is generated in the direction of the arrow 714, betweenthe surface 712 and the underside of the tray 706. This flow produces alower pressure beneath the tray. The pressure differential across theobject in tray results in a net downward force on the object and holdsthe object in the tray, and prevents it from being dislodged byturbulence produced by motion of the ultrasonic transducer or the tray.The flow may be generated, for example, by fluid jets acting on one sideof the tray or by suction acting on one side of the tray.

FIG. 8 is a simplified cross-sectional diagram of a ultrasonic testchamber in accordance with a still further embodiment of the presentinvention. In this embodiment, the scanning station comprises a tank 702containing coupling fluid 704. A tray 706 supports a number of objects708. Typically, the objects are loosely held. An ultrasonic transducer710 is used to scan the objects. A second transducer (not shown) may beused to sense the ultrasound transmitted through the objects. The tray706 is held above a surface 712. Preferably, the surface is flat in thedirection of the scan line of the ultrasonic transducer 710. A flow ofcoupling fluid is generated in the direction of the arrows 716 and 718,between the surface 712 and the underside of the tray 706. The flow isproduced by drawing fluid, from beneath the surface 712, through one ormore holes in the surface. This flow produces a lower pressure beneaththe tray. The pressure differential across the object in tray results ina net downward force on the object and holds the object in the tray,preventing it from being dislodged by turbulence produced by motion ofthe ultrasonic transducer or the tray. Other methods for producing asuitable fluid flow will be apparent to those of ordinary skill in theart.

Retaining Strip. In a further embodiment, where additional force isrequired to hold the parts in the holder at the scanning station, aretaining strip is used. The retaining strip is comprised of acontinuous strip or a series of fingers made out of a spring-likematerial that applies a slight downward pressure to the top of theparts. The fingers are positioned so that they do not cover the parts atthe scan line. Two rows of retaining strips, one prior to and one afterthe scanning line are used.

Scanning Bar (moving cover). In a further embodiment, a flat plate orbar mounted flush with the bottom of the transducer is used to preventthe parts in the holders from being dislodged. The flat plate, referredto as a scanning bar, acts as a barrier between the fluid around thetransducer that is disturbed during motion and the fluid surrounding theparts in the holder. This prevents the disturbed fluid from tending toaffect the position of the parts. If the scanning bar is kept in closeproximity to the top of the holder it will also insure that parts cannot leave the holder in the scanning station. To keep the size and massof the scanning bar small, the scanning bar can be integrated with astationary cover to insure that the parts cannot leave the holder whilein the scanning station.

The above techniques, namely scanning bar, retaining strip,high-pressure and low pressure, can be used in any and all possiblecombinations.

Fixed through-transmission Transducer. Through-transmission teststypically require a transmitter on one side of the part and a receiveron the other side. Typically, both of these transducers will movetogether at the same rate and directions. By using a single element orarray transducer for either the UT transmitter or receiver, only one ofthe two transducers will be in motion thereby reducing the disturbanceto the fluid around the parts and simplifying the mechanics required toimplement a system. In accordance with certain embodiments, the fixedtransducer is located below the holder so that the moving transducer canbe in closer proximity to the parts which is currently a requirement forthe high frequency scans.

Fixed Array (linear and area). If any/all of the ultrasonic transducersrequired are linear or area arrays the speed required can be reducedthereby reducing the tendency for the parts to move or be dislodged fromthe holder. In accordance with certain embodiments, the transducers willcompletely cover the width of a tray and will not be required to move atall. The array could be integrated with a top or bottom cover plate. Thearray could also be used in conjunction with a fixedthrough-transmission transducer.

Integrated Upper Chamber and Scanning Bar. In a further embodiment ofthe scanner, the upper chamber is moved with the ultrasonic transduceras it is scans the object. This allows the upper chamber and thescanning bar to be combined. An embodiment of the upper chamber is shownin FIG. 9. Referring to FIG. 9, the upper chamber 102 comprises a lowerpiece 902 and an upper piece 904. The upper and lower pieces may be heldtogether by fasteners, such as screws 906 or by adhesive, for example.An aperture 908 is provided in the upper piece 904 to allow passage ofan ultrasonic transducer. An aperture 302 in the lower piece 902 allowsfor transmission of the ultrasonic beam to the object being scanned. Amounting hole 910 may be provided to allow for a support structure tohold the ultrasonic transducer in alignment with the upper chamber. Thesection 10-10 is shown in FIG. 10. The use of an upper piece and a lowerpiece facilitate the manufacture of the upper chamber, however, it willbe apparent to those of ordinary skill in the art that the upper chambermay be formed as a single piece or from a plurality of pieces.

A view through the section 10-10 in FIG. 9 is shown in FIG. 10. In FIG.10, an ultrasonic transducer 710 is shown passing through the aperture908 in the upper piece 904. The ultrasonic transducer 710 may be movedvertically with respect to the upper chamber 102 to allow for focusingof the ultrasonic beam at different depths in the object under test.This allows the spacing between the upper chamber 102 and part undertest to be held substantially constant. A fluid cavity 920 is formedbetween the upper piece 904 and the lower piece 902. In operation,coupling fluid in moved into the fluid cavity 920 through fluid inlet922. The coupling fluid exits the fluid cavity 920 through aperture 302in the bottom of the fluid cavity and through aperture 908 in the top ofthe chamber. The bottom surface of the fluid cavity 920 may contain arecess 924 sized to accommodate the ultrasound emitting surface of theultrasonic transducer 710. The thickness of the wall of the fluid cavityin the recess may be less than 1 mm, enabling the ultrasonic transducer710 to be positioned closer to the object being scanned. Thisfacilitates the use of very high frequency ultrasound (with frequenciesfrom a hundred megahertz to several gigahertz or more). The lowersurface of the lower piece 902 may have a lowered section 912. Thislowered section 912 serves a similar purpose to the scanning bardescribed above (104 in FIG. 1).

FIG. 11 is front view of the upper chamber of FIG. 9. In operation,coupling fluid enters the fluid cavity 920 through fluid inlet 922 inthe direction of arrow 930 and exits the fluid cavity 920 throughapertures 908 and 302 in the directions of arrows 932 and 934,respectively. The apertures 908 and 302 may be sized such that there isa resistance to fluid flow when the ultrasonic transducer 710 is placedin the aperture 908. This results in an increased pressure in thecoupling fluid within the fluid cavity 920. The coupling fluid thatexits the aperture 302 in the direction of arrows 934 forms a film orlayer of coupling fluid between the lowered surface 912 and the object106 being scanned. If the spacing between the object 106 being scannedand the lowered surface 912 is small, there will be an increasedpressure in the film of coupling fluid between the lowered surface 912and the object 106. When the object is a loosely held in a tray ofparts, this helps to hold the object in the tray. In general, the filmof coupling fluid effectively removes bubbles from the surface of theobject being scanned. The film of coupling fluid may be less than 1 mmin thick, and the ultrasound emitting surface of the ultrasonictransducer may be positioned less than 1 mm from the surface of theobject being scanned.

The ultrasonic transducer 710 is moveable vertically with respect to theupper chamber 102 in the direction of arrow 936. This allows thetransducer to be focused to different depths within the object 106 beingscanned, while allowing the upper chamber 102 to remain at a constantheight above the object 106. The ultrasonic transducer 710 may be movedusing a linear motion actuator, such as a screw drive. The position ofthe ultrasonic transducer may be adjusted manually or under computercontrol. The bottom surface of the fluid cavity 920 may contain a recess924 sized to accommodate the tip 938 of the ultrasonic transducer 710.This enables the ultrasonic transducer 710 to be positioned closer tothe object being scanned and, in turn, allows higher frequencyultrasound to be used.

The flow of coupling fluid from the fluid cavity 920 out through theaperture 908 dislodges bubbles from the tip 938 of the ultrasonictransducer 710 and allows them to exit through the aperture 908.

FIG. 12 is a side view of a scanning apparatus using the upper chamber102. Referring to FIG. 12, a linear motion device 940, such as screwdrive, is attached to the upper chamber 102. A bracket 942 holds theultrasonic transducer 710 and couples it to the linear motion device940. This allows the ultrasonic transducer 710 to be moved in directionof arrow 936 to focus the ultrasound at the desired depth in the object106 being scanned. In this embodiment, the ultrasonic transducer 710,linear motion device 940 and upper chamber 102 are moved in a horizontalscanning path parallel to the upper surface of the object 106, asindicated by the arrow 944 using one or more additional motion actuators(not shown). Additionally, or alternatively, the object 106 may be movedbeneath upper chamber 102. For example, the upper chamber 102 and theobject 106 may be moved in perpendicular horizontal paths to allow theupper surface of the object to be scanned.

An alternative embodiment of an upper chamber 102 is shown in FIGS. 13and 14. FIG. 13 is a top view of the upper chamber 102 showing an upperpiece 904. An ultrasonic transducer 710 passes through an aperture 908in the upper piece 904. FIG. 14 is sectional view through the section14-14 shown in FIG. 13. FIG. 14 shows upper piece 904 and lower piece902 that together form the fluid cavity 920. In operation, couplingfluid is moved into the fluid cavity 920 through orifice 922. Thecoupling fluid exits the fluid cavity 920 through lower aperture 302 toprovide acoustic coupling to an object being scanned. The coupling fluidalso exits the fluid cavity through the upper aperture 908. Theultrasonic transducer 710 may be moved vertically relative to the upperchamber 102 to allow for focusing of the ultrasonic beam from thetransducer. Recess 924 allows the ultrasonic transducer 710 to be movedto a position in close proximity to the object being scanned. This, inturn, allows higher frequency ultrasonic signals to be used withoutexcessive attenuation. If the transducer if too far from the object, thereflected ultrasonic will be attenuated and more easily corrupted bynoise. An extended lower surface 912 of the upper chamber may be used tocreate a film of coupling fluid above the object being scanned.

A sectional view of a further embodiment of an upper chamber of theinvention is shown in FIG. 15. Referring to FIG. 15, an ultrasonictransducer 710 is shown passing through the aperture 908 in the upperpiece 904. The ultrasonic transducer 710 may be moved vertically withrespect to the upper chamber 102 to allow for focusing of the ultrasonicbeam at different depths in the object under test. This allows thespacing between the upper chamber 102 and part under test to be heldsubstantially constant. A fluid cavity 920 is formed between the upperpiece 904 and the lower piece 902. In operation, coupling fluid in movedinto the fluid cavity 920 through fluid inlet 922. The coupling fluidexits the fluid cavity 920 through aperture 302 in the bottom of thefluid cavity and through aperture 908 in the top of the chamber. Theaperture 302 is sized to accommodate the ultrasound emitting surface ofthe ultrasonic transducer 710, enabling the ultrasonic transducer 710 topass through the aperture and be positioned very close to the objectbeing scanned. This facilitates the use of very high frequencyultrasound (with frequencies from a hundred megahertz to severalgigahertz or more). The ultrasound emitting surface may be positionedflush with the lower surface of the upper chamber, or may protrude belowthe lower surface. The lower surface of the lower piece 902 may have alowered section 912. This lowered section 912 serves a similar purposeto the scanning bar described above (104 in FIG. 1).

In a further embodiment of the invention, the ultrasonic transducer isheld at a fixed position within the upper chamber. In this embodiment,the upper chamber and the ultrasonic transducer are move together toadjust the distance between the ultrasound emitting end of thetransducer and the object being scanned. In this embodiment, the upperaperture 908 may be sealed around the ultrasonic transducer.

The upper chamber 102 shown in FIGS. 9-15 is moved with the ultrasonictransducer 710 along a scanning path as an object 106 is scanned. Itsuse is not limited to scanning objects held in trays. It will beapparent to those of ordinary skill in the art that the upper chambermay be used in a variety of ultrasonic scanning operations to provideacoustic coupling being an ultrasonic transducer and an object beingscanned. In particular, it may be used in the scanning semiconductorwafers, electronic devices and optical devices. A semiconductor wafermay be held in a wafer chuck, such as a vacuum chuck, while undergoingscanning. The wafer may be moved relative to the upper chamber duringscanning or vice versa.

DRYER. After the ultrasonic scanning of the parts in the holder iscompleted, it is desirable to remove the coupling fluid from the partsto prevent the fluid from affecting the quality or appearance (i.e.water spots) of the parts. The dryer of the present invention includesone or more of the following:

Gas Stream. A gas stream can be used to dry any residual coupling fluidfrom the parts. Typically compressed and/or heated air is directedacross the parts. By using a vacuum or suction from beneath the holder,drying gas will still flow across the parts but it will tend to hold theparts in the holder rather than dislodge them. Additionally, anair-knife can be used to blow residual fluid from the upper surface ofthe parts.

Wicking Material. If any liquid residue is left on parts, a wickingmaterial may be placed in contact with the part to remove the moisture.

Brush. If any liquid residue is left on parts, the parts may be passedunder a brush, so that bristles of the brush contact with the part andremove the moisture. Preferably, the brush contacts the lower surface ofthe part.

While the invention has been particularly shown and described withreference to exemplary embodiments, it will be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention. Inaddition, it is evident that many alternatives, modifications,permutations and variations will become apparent to those of ordinaryskill in the art in light of the foregoing description. Accordingly, itis intended that the present invention embrace all such alternatives,modifications and variations as fall within the scope of the appendedclaims.

1. A method for coupling ultrasound between an ultrasonic transducer andan object, the method comprising: positioning an upper chamber and theobject in close proximity to each other; positioning an ultrasoundemitting surface of the ultrasonic transducer in a fluid cavity of theupper chamber, the fluid cavity having a lower aperture; moving theultrasonic transducer relative to the upper chamber to adjust the focusof the ultrasound; supplying a coupling fluid to the fluid cavity sothat coupling fluid flows through the lower aperture of the fluid cavityonto the object; and insonifing the object with ultrasound from theultrasonic transducer.
 2. A method in accordance with claim 1, furthercomprising moving the ultrasonic transducer and the upper chamber in ascan path substantially parallel to a surface of the object, whereinmoving the ultrasonic transducer relative to the upper chamber to adjustthe focus of the ultrasound comprises moving the ultrasonic transducerin a direction substantially perpendicular to the scan path.
 3. A methodin accordance with claim 2, further comprising adjusting the separationbetween the upper chamber and the object to form a thin layer ofcoupling fluid between a lower surface of the upper chamber and an uppersurface of the object.
 4. A method in accordance with claim 1, whereinthe ultrasonic transducer passes through an upper aperture of the fluidcavity and further comprising flowing coupling fluid across theultrasound emitting surface of the ultrasonic transducer to exit throughthe upper aperture and remove bubbles from the ultrasound emittingsurface of the ultrasonic transducer.
 5. A method in accordance withclaim 1, further comprising collecting coupling fluid dispensed from theupper chamber in a lower chamber positioned beneath the object.
 6. Amethod in accordance with claim 1, wherein moving the ultrasonictransducer relative to the upper chamber to adjust the focus of theultrasound comprises moving the ultrasonic transducer through the loweraperture.
 7. A method for coupling ultrasound between an ultrasonictransducer and an object, the method comprising: positioning an upperchamber and the object in close proximity to each other; positioning theultrasonic transducer in a fluid cavity of the upper chamber, the fluidcavity having a lower aperture, the ultrasonic transducer having anultrasound emitting end that passes at least partially through the loweraperture; moving the ultrasonic transducer relative to the upper chamberto adjust the focus of the ultrasound; supplying a coupling fluid to thefluid cavity so that coupling fluid flows through the lower aperture ofthe fluid cavity onto the object; and insonifying the object withultrasound from the ultrasonic transducer.
 8. An apparatus for couplingultrasound to an object, comprising: an ultrasonic transducer having asurface operable to emit an ultrasound beam; and an upper chambercontaining a fluid cavity, the upper chamber having a fluid inlet forreceiving coupling fluid, a first aperture for receiving the ultrasonictransducer and a second aperture for dispensing the coupling fluid to asurface of the object; wherein the ultrasound emitting surface of theultrasonic transducer is moveable within the fluid cavity to adjust afocal point of the ultrasound emitted from the surface of the ultrasonictransducer.
 9. An apparatus in accordance with claim 8, wherein aportion of the lower surface of the fluid cavity is recessed toaccommodate the surface of the ultrasonic transducer that is operable toemit ultrasound.
 10. An apparatus in accordance with claim 8, whereinultrasound from the ultrasonic transducer passes through the secondaperture to a position close to the surface of the object.
 11. Anapparatus in accordance with claim 8, further comprising a linear motiondevice operable to move the ultrasonic transducer relative to the upperchamber.
 12. An apparatus in accordance with claim 8, further comprisingat least one motion actuator for moving the ultrasonic transducer andthe upper chamber in a scan path substantially parallel to the surfaceof the object.
 13. An apparatus in accordance with claim 8, wherein theobject comprises a part of a plurality of parts supported in a partstray.
 14. An apparatus in accordance with claim 13, further comprising atrack operable to support the parts tray and move through it through theultrasonic beam.
 15. An apparatus in accordance with claim 8, whereinthe object comprises a semiconductor wafer held in wafer chuck.
 16. Anapparatus in accordance with claim 8, wherein the object comprises amicroelectronic device.
 17. An apparatus in accordance with claim 8,wherein the object comprises an optical device.
 18. An apparatus inaccordance with claim 8, wherein a bottom surface of the upper chamberis flat so as to constrain the coupling fluid in a thin layer betweenthe bottom surface and of the upper chamber and an upper surface of theobject when the bottom surface of the upper chamber is placed in closeproximity to the object.
 19. An apparatus in accordance with claim 8,further comprising a lower chamber positioned beneath the object forcollecting coupling fluid dispensed from the upper chamber.
 20. Anapparatus in accordance with claim 8, wherein the ultrasonic transducerpasses through the second aperture to a position close to the object.21. An apparatus for coupling ultrasound between an ultrasonictransducer and an object, comprising: a chamber adapted to substantiallyenclose an ultrasound transmitting surface of the ultrasonic transducerto form a fluid cavity; a fluid inlet in the fluid cavity for receivinga flow of coupling fluid; a first aperture for admitting the ultrasonictransducer into the fluid cavity; and a second aperture for dispensingcoupling fluid from the fluid cavity to the object; wherein the firstand second apertures are sized to restrict flow of coupling fluid fromthe fluid cavity.
 22. An apparatus in accordance with claim 21, furthercomprising: an ultrasonic transducer operable to generate ultrasound;and a linear motion device for positioning the ultrasonic transducerrelative to the chamber to facilitate focusing of the ultrasound in theobject.
 23. An apparatus in accordance with claim 22, wherein theultrasound passes between the ultrasonic transducer and the objectthrough the second aperture.
 24. An apparatus in accordance with claim22, wherein the ultrasound has a frequency greater than 100 MHz.
 25. Anapparatus in accordance with claim 22, wherein the ultrasound has afrequency greater than 500 MHz.
 26. An apparatus in accordance withclaim 21, wherein the first and second apertures are coaxially aligned.27. An apparatus in accordance with claim 21, wherein a lower wall ofthe chamber in proximity to the ultrasound transmitting surface of theultrasonic transducer is less than 1 mm thick, allowing the ultrasoundtransmitting surface of the ultrasonic transducer to be placed in closeproximity to the object.
 28. An apparatus in accordance with claim 21,wherein a bottom surface of the chamber is flat so as to constrain thecoupling fluid in a thin layer between the bottom surface and of thechamber and an upper surface of the object when the bottom surface ofthe chamber is placed in close proximity to the object.
 29. An apparatusfor coupling ultrasound to an object, comprising: an ultrasonictransducer having a surface operable to emit an ultrasound beam; and anupper chamber containing a fluid cavity, the upper chamber having afluid inlet for receiving coupling fluid, a first aperture for receivingthe ultrasonic transducer and a second aperture for dispensing thecoupling fluid to a surface of the object; wherein the upper chamber andthe ultrasonic transducer are moveable to adjust a focal point of theultrasound emitted from the surface of the ultrasonic transducer.
 30. Anapparatus in accordance with claim 29, wherein a lower wall of thechamber in proximity to the ultrasound emitting surface of theultrasonic transducer is less than 1 mm thick, allowing the ultrasoundemitting surface of the ultrasonic transducer to be placed in closeproximity to the object.
 31. An apparatus in accordance with claim 29,wherein the ultrasonic transducer passes through the second aperture toa position close to the object.
 32. An apparatus in accordance withclaim 29, wherein the second aperture is sized to restrict flow ofcoupling fluid from the fluid cavity.